The Nyaya school is astika, orthodox, in the sense that they accepted the vedas. At the very start of the Bhasha Pariccheda with Siddhanta-Muktavali by Visvanatha-Nyaya-Pancanana (translation by Swami Madhavananda) the opening invocation is from the vedas. And in his opening commentary Visvanatha-Nyaya-Pancanana states:
...The invocation there is made in apprehension of an obstacle; for such is the practice among the cultured. Nor can it be urged that if an invocation is fruitless, the Vedas inculcating it cease to be authoritative; for the Vedas only say that if there be an obstacle, it will be removed (in that way). Hence although as expiatory ceremony that is performed for an act wrongly apprehended is futile, yet it does not nullify the authoritativeness of the Vedas that teach it...
And at the end of the commentary on this opening invocation, Visvanatha-Nyaya-Pancanana quotes Rig Veda X.lxxx.3 'One shining Being generating heaven and earth' and Mundakya Upanishad I.i.1 'The creator of the universe, the protector of the universe'
And as they accept the vedas, one only need look at the concluding verses of several of the Upanishads that they are directly from Brahman (for example Brhadaranyaka Upanishad VI.v.3, and Chandogya Upanishad VIII.15.1).